Bearings for such types of assemblies, such as in tunnel drilling machines, often have large dimensions. To facilitate mounting and dismounting the bearings, they are often mounted with a loose fit on the shaft, although the rotating load occurring during operation in relation to the inner race rings of the bearing, according to normal regulations, requires an interference fit between the inner race rings and the shaft. According to recommendations from bearing manufacturers, a tolerance choice of about r7 for shaft diameters larger than 500 mm is recommended. One of the drawbacks of the loose fit used contrary to the recommendations is that wear will occur on shaft and axial supporting surfaces.
In tunnel drilling machines, the axial loads occurring during operation are very large, whereby the bearings are often assembled in preloaded condition to better compensate for the increasing play occurring in the bearing due to the elastic deflection of the bearing during drilling. If the axial supporting surfaces of the bearings are subjected to wear, the preload on the bearings is decreased.